USB: prevent char device open/deregister race

This patch (as908) adds central protection in usbcore for the
prototypical race between opening and unregistering a char device.
The spinlock used to protect the minor-numbers array is replaced with
an rwsem, which can remain locked across a call to a driver's open()
method.  This guarantees that open() and deregister() will be mutually
exclusive.

The private locks currently used in several individual drivers for
this purpose are no longer necessary, and the patch removes them.  The
following USB drivers are affected: usblcd, idmouse, auerswald,
legousbtower, sisusbvga/sisusb, ldusb, adutux, iowarrior, and
usb-skeleton.

As a side effect of this change, usb_deregister_dev() must not be
called while holding a lock that is acquired by open().  Unfortunately
a number of drivers do this, but luckily the solution is simple: call
usb_deregister_dev() before acquiring the lock.

In addition to these changes (and their consequent code
simplifications), the patch fixes a use-after-free bug in adutux and a
race between open() and release() in iowarrior.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

3 files changed, 7 insertions, 58 deletions

diff --git a/drivers/usb/misc/sisusbvga/sisusb.c b/drivers/usb/misc/sisusbvga/sisusb.c
index 6f8b134a79c..9f37ba44c13 100644
--- a/drivers/usb/misc/sisusbvga/sisusb.c
+++ b/drivers/usb/misc/sisusbvga/sisusb.c
@@ -72,8 +72,6 @@ MODULE_PARM_DESC(last, "Number of last console to take over (1 - MAX_NR_CONSOLES
 
 static struct usb_driver sisusb_driver;
 
-DEFINE_MUTEX(disconnect_mutex);
-
 static void
 sisusb_free_buffers(struct sisusb_usb_data *sisusb)
 {
@@ -2511,31 +2509,24 @@ sisusb_open(struct inode *inode, struct file *file)
 	struct usb_interface *interface;
 	int subminor = iminor(inode);
 
-	mutex_lock(&disconnect_mutex);
-
 	if (!(interface = usb_find_interface(&sisusb_driver, subminor))) {
 		printk(KERN_ERR "sisusb[%d]: Failed to find interface\n",
 				subminor);
-		mutex_unlock(&disconnect_mutex);
 		return -ENODEV;
 	}
 
-	if (!(sisusb = usb_get_intfdata(interface))) {
-		mutex_unlock(&disconnect_mutex);
+	if (!(sisusb = usb_get_intfdata(interface)))
 		return -ENODEV;
-	}
 
 	mutex_lock(&sisusb->lock);
 
 	if (!sisusb->present || !sisusb->ready) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return -ENODEV;
 	}
 
 	if (sisusb->isopen) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return -EBUSY;
 	}
 
@@ -2543,7 +2534,6 @@ sisusb_open(struct inode *inode, struct file *file)
 		if (sisusb->sisusb_dev->speed == USB_SPEED_HIGH) {
 			if (sisusb_init_gfxdevice(sisusb, 0)) {
 				mutex_unlock(&sisusb->lock);
-				mutex_unlock(&disconnect_mutex);
 				printk(KERN_ERR
 					"sisusbvga[%d]: Failed to initialize "
 					"device\n",
@@ -2552,7 +2542,6 @@ sisusb_open(struct inode *inode, struct file *file)
 			}
 		} else {
 			mutex_unlock(&sisusb->lock);
-			mutex_unlock(&disconnect_mutex);
 			printk(KERN_ERR
 				"sisusbvga[%d]: Device not attached to "
 				"USB 2.0 hub\n",
@@ -2570,8 +2559,6 @@ sisusb_open(struct inode *inode, struct file *file)
 
 	mutex_unlock(&sisusb->lock);
 
-	mutex_unlock(&disconnect_mutex);
-
 	return 0;
 }
 
@@ -2601,12 +2588,8 @@ sisusb_release(struct inode *inode, struct file *file)
 	struct sisusb_usb_data *sisusb;
 	int myminor;
 
-	mutex_lock(&disconnect_mutex);
-
-	if (!(sisusb = (struct sisusb_usb_data *)file->private_data)) {
-		mutex_unlock(&disconnect_mutex);
+	if (!(sisusb = (struct sisusb_usb_data *)file->private_data))
 		return -ENODEV;
-	}
 
 	mutex_lock(&sisusb->lock);
 
@@ -2626,8 +2609,6 @@ sisusb_release(struct inode *inode, struct file *file)
 	/* decrement the usage count on our device */
 	kref_put(&sisusb->kref, sisusb_delete);
 
-	mutex_unlock(&disconnect_mutex);
-
 	return 0;
 }
 
@@ -3383,12 +3364,9 @@ static void sisusb_disconnect(struct usb_interface *intf)
 	sisusb_console_exit(sisusb);
 #endif
 
-	/* The above code doesn't need the disconnect
-	 * semaphore to be down; its meaning is to
-	 * protect all other routines from the disconnect
-	 * case, not the other way round.
-	 */
-	mutex_lock(&disconnect_mutex);
+	minor = sisusb->minor;
+
+	usb_deregister_dev(intf, &usb_sisusb_class);
 
 	mutex_lock(&sisusb->lock);
 
@@ -3396,12 +3374,8 @@ static void sisusb_disconnect(struct usb_interface *intf)
 	if (!sisusb_wait_all_out_complete(sisusb))
 		sisusb_kill_all_busy(sisusb);
 
-	minor = sisusb->minor;
-
 	usb_set_intfdata(intf, NULL);
 
-	usb_deregister_dev(intf, &usb_sisusb_class);
-
 #ifdef SISUSB_OLD_CONFIG_COMPAT
 	if (sisusb->ioctl32registered) {
 		int ret;
@@ -3426,8 +3400,6 @@ static void sisusb_disconnect(struct usb_interface *intf)
 	/* decrement our usage count */
 	kref_put(&sisusb->kref, sisusb_delete);
 
-	mutex_unlock(&disconnect_mutex);
-
 	printk(KERN_INFO "sisusbvga[%d]: Disconnected\n", minor);
 }
 
diff --git a/drivers/usb/misc/sisusbvga/sisusb_con.c b/drivers/usb/misc/sisusbvga/sisusb_con.c
index 5947afb0017..8d0edc867f3 100644
--- a/drivers/usb/misc/sisusbvga/sisusb_con.c
+++ b/drivers/usb/misc/sisusbvga/sisusb_con.c
@@ -214,18 +214,13 @@ sisusbcon_init(struct vc_data *c, int init)
 	 * are set up/restored.
 	 */
 
-	mutex_lock(&disconnect_mutex);
-
-	if (!(sisusb = sisusb_get_sisusb(c->vc_num))) {
-		mutex_unlock(&disconnect_mutex);
+	if (!(sisusb = sisusb_get_sisusb(c->vc_num)))
 		return;
-	}
 
 	mutex_lock(&sisusb->lock);
 
 	if (!sisusb_sisusb_valid(sisusb)) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return;
 	}
 
@@ -264,8 +259,6 @@ sisusbcon_init(struct vc_data *c, int init)
 
 	mutex_unlock(&sisusb->lock);
 
-	mutex_unlock(&disconnect_mutex);
-
 	if (init) {
 		c->vc_cols = cols;
 		c->vc_rows = rows;
@@ -284,12 +277,8 @@ sisusbcon_deinit(struct vc_data *c)
 	 * and others, ie not under our control.
 	 */
 
-	mutex_lock(&disconnect_mutex);
-
-	if (!(sisusb = sisusb_get_sisusb(c->vc_num))) {
-		mutex_unlock(&disconnect_mutex);
+	if (!(sisusb = sisusb_get_sisusb(c->vc_num)))
 		return;
-	}
 
 	mutex_lock(&sisusb->lock);
 
@@ -314,8 +303,6 @@ sisusbcon_deinit(struct vc_data *c)
 
 	/* decrement the usage count on our sisusb */
 	kref_put(&sisusb->kref, sisusb_delete);
-
-	mutex_unlock(&disconnect_mutex);
 }
 
 /* interface routine */
@@ -1490,14 +1477,11 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 {
 	int i, ret, minor = sisusb->minor;
 
-	mutex_lock(&disconnect_mutex);
-
 	mutex_lock(&sisusb->lock);
 
 	/* Erm.. that should not happen */
 	if (sisusb->haveconsole || !sisusb->SiS_Pr) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return 1;
 	}
 
@@ -1508,14 +1492,12 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 	    first > MAX_NR_CONSOLES ||
 	    last > MAX_NR_CONSOLES) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return 1;
 	}
 
 	/* If gfxcore not initialized or no consoles given, quit graciously */
 	if (!sisusb->gfxinit || first < 1 || last < 1) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return 0;
 	}
 
@@ -1526,7 +1508,6 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 	/* Set up text mode (and upload  default font) */
 	if (sisusb_reset_text_mode(sisusb, 1)) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		printk(KERN_ERR
 			"sisusbvga[%d]: Failed to set up text mode\n",
 			minor);
@@ -1550,7 +1531,6 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 	/* Allocate screen buffer */
 	if (!(sisusb->scrbuf = (unsigned long)vmalloc(sisusb->scrbuf_size))) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		printk(KERN_ERR
 			"sisusbvga[%d]: Failed to allocate screen buffer\n",
 			minor);
@@ -1558,7 +1538,6 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 	}
 
 	mutex_unlock(&sisusb->lock);
-	mutex_unlock(&disconnect_mutex);
 
 	/* Now grab the desired console(s) */
 	ret = take_over_console(&sisusb_con, first - 1, last - 1, 0);
diff --git a/drivers/usb/misc/sisusbvga/sisusb_init.h b/drivers/usb/misc/sisusbvga/sisusb_init.h
index f05f83268af..864bc0e9659 100644
--- a/drivers/usb/misc/sisusbvga/sisusb_init.h
+++ b/drivers/usb/misc/sisusbvga/sisusb_init.h
@@ -808,8 +808,6 @@ static const struct SiS_VCLKData SiSUSB_VCLKData[] =
 	{ 0x2b,0xc2, 35}  /* 0x71 768@576@60 */
 };
 
-extern struct mutex disconnect_mutex;
-
 int		SiSUSBSetMode(struct SiS_Private *SiS_Pr, unsigned short ModeNo);
 int		SiSUSBSetVESAMode(struct SiS_Private *SiS_Pr, unsigned short VModeNo);